Black Hole Interactions and Neutron star Collisions Across the universe

Informations projet

BHianca

N° de convention de subvention: 101002761

DOI

10.3030/101002761

Date de signature de la CE 14 Juillet 2021

Date de début 1 Janvier 2022

Date de fin 31 Decembre 2026

Financé au titre de

• EXCELLENT SCIENCE - European Research Council (ERC)

Coût total

€ 1 974 000,00

Contribution de l’UE

€ 1 974 000,00

Coordonné par

UNIVERSITA DEGLI STUDI DI ROMA TOR VERGATA
Italy

Periodic Reporting for period 2 - BHianca (Black Hole Interactions and Neutron star Collisions Across the universe)

Période du rapport: 2023-07-01 au 2024-12-31

Résumé du contexte et des objectifs généraux du projet

Since the dawn of civilization our knowledge of the cosmos has been dominated by a single type of signal: electromagnetic radiation (that is, light). However, light interacts with matter and, for this reason, it often remains trapped within the celestial objects we wish to study. Only the radiation produced in the outermost layers can escape and reach us. Through light, we are just scratching the surface of our Universe.
The blossoming field of multi-messenger astrophysics opens a new window onto the invisible Universe, in which different cosmic messengers - such as gravitational waves, neutrinos and light - provide complementary views of the same source. We can learn more from the Universe by combining these multiple messengers, just as we combine colors, sounds and flavors to know about the world. Gravitational waves and neutrinos probe the innermost regions - impenetrable to light - of extreme astrophysical events, and carry unique information about the behavior of masses and the production of energy. These novel astrophysical observations allow us to move beyond the realm usually probed by light, transforming our way to think about the Universe.

This ERC project aims at understanding the violent encounters of the densest objects in the Universe, such as neutron stars (NSs) and black holes (BHs). These extreme stellar collisions create gravitational waves and light that we will combine to address some of the most fundamental questions of modern astrophysics: from the exotic states of matter at supra-nuclear densities to the expansion rate of the Universe and the origin of the heaviest metals, such as gold and platinum. Breakthrough results will be achieved by making first detections of light from NS-NS and NS-BH encounters in our cosmic backyard.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

The work is organized in three interlinked work packages addressing 1) how black holes burp out their energy 2) what are the cosmic factories forging metals heavier than iron, and 3) how these stellar mergers can teach us more about fundametal physics and cosmology. Over the first period, the PI devoted most of her efforts in setting up the group and securing the observational resources. Nonetheless, progress has been made in all three main areas.

The project was inaugurated by the discovery of GRB211211A, a minute-long explosion followed by a glow of red light known as kilonova. The kilonova is the telltale signature for the production of radioactive heavy nuclei via rapid neutron capture processes (WP2). However, a kilonova is a rare event that only happens with a neutron star encounters another compact object such as another neutron star or a black hole. The association of a kilonova with a long GRB shows that not all long GRBs are the product of the explosive death of a massive star, challenging our long-established beliefs about how long GRBs and their progenitors.
The PI had a central role in the discovery and characterization of the kilonova, the results of her research were published on December 7 in the journal Nature.

A few months later we were surprised by the brightest gamma-ray burst (GRB) ever observed, GRB221009A, which pushed our models to the extreme. This titanic explosion surpassed in brightness any previous gamma-ray burst and was so bright it effectively blinded most gamma-ray instruments in space. All this energy was shot into space in the form of a jet by a black hole, born in the GRB explosion. In just about every previously observed gamma-ray burst, the jet remained remarkably compact and there was little to no stray light or material outside the narrow beam. By contrast, in GRB 221009A the jet had a narrow core with wider, sloping sides. These properties, also shared by a small group of insanely bright bursts, allow us a better understanding of how black holes release their power through ultra-fast jets (WP1).
The PI and her team had a central role in this study, which was published on June 7 in the journal Science Advances.

Finally, we have been using the peculiar explosion dubbed GRB230307A to probe the interior of neutron stars (WP3) and to provide direct evidence for the production for heavy metals (WP2).
We investigated what happens before two compact objects collide, what sort of electromagnetic radiation may become visible and how its brightness and duration depend on the behavior of matter in extreme conditions.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Gamma-ray bursts (GRBs) are the high-energy radiation arising from immense cosmic blasts of gamma rays and serve as a signature for different types of dying stars. For decades, astronomers believed they had a good grasp of the basic nature of GRBs: bursts of long duration – lasting more than 2 seconds – happen when a massive star reaches the end of its life. On the other hand, short-duration bursts of less than 2 seconds occur when two hyper-dense objects, such as two neutron stars, collide, blasting immense energy in an explosion known as a kilonova. Our discovery of a long duration GRB followed by a kilonova is causing scientists to rethink what they know about short- and long-duration GRBs. We can no longer assume that all long-duration bursts come exclusively from massive stars, and need to think of new ways to produce a long lasting blast of gamma-rays from the encounter of two compact objects.

In the next two years, breakthrough discoveries are to be expected. The reactivation of the LIGO detectors marked the beginning of the O4 observing run, when gravitational wave detectors will chase NS-NS and NS-BH in the nearby Universe with a predicted tenfold improvement in discovery rates. We will observe new GW sources with the goal of finding their electromagnetic counterparts, thus discovering the next multi-messenger source.
By combining gravitational waves and electromagnetic radiation, we can learn more information about our cosmic history than any one of these messengers can provide in isolation. These multi-messenger events will reveal the Universe as never before.

The long duration GRB211211A and its red kilonova. Credit: NOIRLab/NASA/ESA/E. Troja